Quinoxaline derivative, and organic semiconductor device, electric field light emitting device, and electronic device which have the same

ABSTRACT

Target is to provide an organic compound material having a bipolar character. 
     A quinoxaline derivative represented by a general formula (1) is provided. In the formula, R 1 -R 12  each independently represents a hydrogen atom, a halogen atom, a lower alkyl group, an alkoxy group, an acyl group, a nitro group, a cyano group, an amino group, a dialkylamino group, a diarylamino group, a vinyl group, an aryl group, or a heterocyclic residue group. R 9  and R 10 , R 10  and R 11 , and R 11  and R 12  are each independent or respectively mutually bonded to form an aromatic ring. Ar 1 -Ar 4  each independently represents an aryl group or a heterocyclic residue group. Ar 1 , Ar 2 , Ar 3  and Ar 4  are each independent or Ar l  and Ar 2 , and Ar 3  and Ar 4  are respectively mutually bonded directly, or Ar 1  and Ar 3 , and Ar 3  and Ar 4  are bonded via oxygen (O), sulfur (S) or a carbonyl group.

This application is a divisional of application Ser. No. 10/826,838filed on Apr. 16, 2004 now U.S. Pat. No. 7,601,435.

TECHNICAL FIELD

The present invention relates to a quinoxaline derivative which is anorganic compound material, and an organic semiconductor device utilizingthe same. It also relates to an electric field light emitting deviceutilizing the aforementioned quinoxaline derivative.

BACKGROUND OF THE INVENTION

Organic compounds include more varied material systems in comparisonwith inorganic compounds, and have possibility that materials of variousfunctions can be synthesized by an appropriate molecular design. Alsothey have features that a molded article such as a film is flexible andprovides an excellent workability by a polymer formation. Based on theseadvantages, photonics and electronics utilizing functional organicmaterials are attracting attention recently.

Examples of an electronic device utilizing an organic compound materialas a functional organic material include a solar cell, an electric fieldlight emitting device, and an organic transistor. These are devicesutilizing electrophysical properties (carrier transporting property) andoptophysical properties (light absorption or emission) of the organiccompound material, and, among these, the electric field light emittingdevice is showing a remarkable progress.

As a most basic device structure of the electric field light emittingdevice, there is known a structure in which a thin film of a totalthickness of about 100 nm, formed by a hole transporting layerconstituted of a hole transporting organic compound and an electrontransporting light-emitting layer constituted of an electrontransporting organic compound, is sandwiched between electrodes (forexample cf. non-patent reference 1). By applying a voltage on suchdevice, a light emission can be obtained from the electron transportingorganic compound which also has a light emitting property. Suchstructure is generally called a single hetero (SH) structure.

The electric field light emitting device in the non-patent reference 1can be considered to be based on a functional separation, namely thetransportation of holes being executed by the hole transport layer andthe transportation of electrons being executed by the electron transportlayer.

Thereafter, for the purposes of further improvement in a change of anemission spectrum and a decrease in the light emission efficiencyresulting from an interaction (for example formation of an exciplex) atan interface of the laminated layer, the concept of such functionalseparation has been developed into a double hetero (DH) structure inwhich a light emitting layer is inserted between the hole transportlayer and the electron transport layer (for example cf. non-patentreference 2).

In an electric field light emitting device as described in thenon-patent reference 2, in order to further suppress an interactiongenerated at the interface, it is preferable to form the light emittinglayer with a bipolar material having both the electron transportingproperty and the hole transporting property.

However, organic compound materials are mostly a monopolar material,having either the hole transporting property or the electrontransporting property. For example, a material shown in the followingpatent reference 1 is only applied as an electron injecting layer.

It is therefore desired to newly develop an organic compound materialhaving a bipolar character.

-   Patent reference 1: JP-A-2003-40873-   Non-patent reference 1: C. W. Tang and one another, Applied Physics    Letters, Vol. 51, No. 12, 913-915 (1987)-   Non-patent reference 2: Chihaya Adachi and three others, Japanese    Journal of Applied Physics, Vol. 27, No. 2, L269-L271 (1988).

SUMMARY OF THE INVENTION

A target of the present invention is to provide an organic compoundmaterial having a bipolar property and also a light emitting property.It is also a target to provide an organic semiconductor device utilizingsuch organic compound material, particularly an electric field lightemitting device capable of reducing a device failure such as adielectric breakdown or improving a light emitting property by employingthe aforementioned organic compound material.

MEANS FOR SOLVING THE PROBLEMS

The present invention provides a quinoxaline derivative represented by ageneral formula (1).

In the formula (1), R¹-R¹² may be same or different and each representsa hydrogen atom, a halogen atom, a lower alkyl group, an alkoxy group,an acyl group, a nitro group, a cyano group, an amino group, adialkylamino group, a diarylamino group, a vinyl group that may have asubstituent, an aryl group that may have a substituent, or aheterocyclic residue group that may have a substituent. Also, R⁹ andR¹⁰, R¹⁰ and R¹¹, or R¹¹ and R¹² may be mutually bonded to form anaromatic ring. Also Ar¹-Ar⁴ may be same or different and each representsan aryl group that may have a substituent or a heterocyclic residuegroup that may have a substituent. Also Ar¹ and Ar², and Ar³ and Ar⁴ maybe mutually bonded directly as shown in a following general formula(68), or bonded via oxygen (O), sulfur (S) or a carbonyl group as shownin a following general formula (69).

In the formula (68), R¹ to R¹² are same as shown in the formula (1).

In the formula (69), A and B represent oxygen (O), sulfur (S), or acarbonyl group. Also R¹ to R¹² are same as shown in the formula (1).

The present invention provides a quinoxaline derivative represented by ageneral formula (2).

In the formula (2), X and Y each is represented by either one offormulas (3)-(5).

In the formulas, R¹-R³⁸ may be same or different and each represents ahydrogen atom, a halogen atom, a lower alkyl group, an alkoxy group, anacyl group, a nitro group, a cyano group, an amino group, a dialkylaminogroup, a diarylamino group, a vinyl group that may have a substituent,an aryl group that may have a substituent, or a heterocyclic residuegroup that may have a substituent. Also, R⁹ and R¹⁰, R¹⁰ and R¹¹, or R¹¹and R¹² may be mutually bonded to form an aromatic ring. Z representsoxygen (O), sulfur (S) or a carbonyl group.

The present invention provides a quinoxaline derivative represented by ageneral formula (6).

In the formula (6), X and Y each is represented by either one offormulas (7)-(9).

In the formulas, R⁹-R¹² may be same or different and each represents ahydrogen atom, a halogen atom, a lower alkyl group, an alkoxy group, anacyl group, a nitro group, a cyano group, an amino group, a dialkylaminogroup, a diarylamino group, a vinyl group that may have a substituent,an aryl group that may have a substituent, or a heterocyclic residuegroup that may have a substituent. Also, R⁹ and R¹⁰, R¹⁰ and R¹¹, or R¹¹and R¹² may be mutually bonded to form an aromatic ring. Z representsoxygen (O), sulfur (S) or a carbonyl group.

In the foregoing general formulas (1), (2) and (6), the lower alkylgroup can be a methyl group, an ethyl group, an n-propyl group, anisopropyl group, an n-butyl group, a sec-butyl group, a tert-butylgroup, or a hexyl group and preferably includes 1-6 carbon atoms. It canalso be a halogenated alkyl group such as a trifluoromethyl group, or acycloalkyl group such as a cyclohexyl group. The alkoxy group can be amethoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group,an n-butoxy group, a sec-butoxy group, a tert-butoxy group or a hexoxygroup, and preferably includes 1-6 carbon atoms. The acyl group can bean acetyl group or the like. The dialkylamino group can be adimethylamino group, a diethylamino group or the like, preferablycontaining 1-4 carbon atoms in the alkyl chain. The diarylamino groupcan be a diphenylamino group, a bis(α-naphthyl)amino group or the like,and also be a substituted arylamino group such as a bis(m-tolyl)aminogroup. The vinyl group may also be a vinyl group having a substituentsuch as a diphenylvinyl group. The aryl group can be not only anon-substituted aryl group such as a phenyl group or a naphthyl group,but also a substituted aryl group such as an o-tolyl group, an m-tolylgroup, a p-tolyl group, a xylyl group, a methoxyphenyl group, anethoxyphenyl group or a fluorophenyl group. The heterocyclic residuegroup can be a pyridyl group, a furyl group, a thienyl group or thelike, which may further have a substituent such as a methyl group.

In the following, specific structural formulas of the quinoxalinederivative of the present invention are listed, but the presentinvention is not limited to these.

The aforementioned quinoxaline derivative of the present invention has abipolar property and also a light emitting property. Also not easilycontaining a microcrystalline component at a film formation by anevaporation method, it has a satisfactory film forming property.

An example of a synthesizing method for the quinoxaline derivative ofthe present invention will be shown, taking the compound represented bythe structural formula (10) above as an example. The quinoxalinederivative represented by the structural formula (10) above of thepresent invention can be obtained, for example, by a followingsynthesizing scheme.

Also other compounds can be obtained, as shown above, by a methodutilizing a dibromo compound of diphenylquinoxaline. However, the methodfor synthesizing the quinoxaline derivative of the present invention isnot limited to such method.

Another structure of the present invention is an organic semiconductordevice utilizing the quinoxaline derivative represented by the generalformula (1), (2) or (6).

The organic semiconductor device can be, for example, an electric fieldlight emitting device, an organic transistor, or an organic solar cell.

Another structure of the present invention is an electric field lightemitting device characterized in including a quinoxaline derivativerepresented by the general formula (1), (2) or (6) between a pair ofelectrodes.

The quinoxaline derivative of the present invention, having a bipolarproperty and a light emitting property, can be used as a light emittinglayer of an electric field light emitting device, without particularlyincluding a dopant (guest material). Also owing to the bipolar property,the light emitting portion is not easily deviated at the interface ofthe laminated films, and an electric field light emitting device of asatisfactory light emitting property can be prepared with little changein the light emission spectrum and little decrease in the light emissionefficiency resulting from an interaction such as an exciplex.

The quinoxaline derivative of the present invention, having a lightemitting property, can be employed as a guest material (light emittingmember) in the light emitting layer of the electric field light emittingdevice.

Also the quinoxaline derivative of the present invention, having abipolar property and not easily containing a microcrystalline componentat a film formation thereby showing a satisfactory film formingproperty, can be employed as a host material in the light emitting layerof the electric field light emitting device. In case of use as the hostmaterial, there can be obtained a light emission color resulting from aguest material, or a mixed light emission color of a light emissioncolor resulting from the quinoxaline derivative of the present inventionand a light emission color resulting from the guest material.

Particularly in case the quinoxaline derivative of the present inventionis employed as a host material, a phosphorescent material showing alight emission from a triplet excited state is used as the guestmaterial to obtain an electric field light emitting device of a highcurrent efficiency and a low driving voltage. Therefore, an electricfield light emitting device having the light emitting layer containingthe quinoxaline derivative of the present invention and a phosphorescentmaterial showing a light emission from a triplet excited state is alsoincluded in the present invention. In such case, the phosphorescentmaterial preferably has a peak of a light emission spectrum from 560 to700 nm.

EFFECT OF THE INVENTION

The present invention allows to obtain a quinoxaline derivative having abipolar property and a light emitting property. Also the use of thequinoxaline derivative of the present invention allows to prepare anelectric field light emitting device in which the light emitting portionis not easily deviated at the interface of the laminated films, andwhich shows a satisfactory light emitting property with little change inthe light emission spectrum and little decrease in the light emissionefficiency resulting from an interaction such as an exciplex.Furthermore, the use of the quinoxaline derivative of the presentinvention allows to prepare a satisfactory electric field light emittingdevice with little device defects such as a dielectric breakdown by anelectric field concentration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for explaining one aspect of an electric field lightemitting device of the present invention.

FIG. 2 is a view for explaining one aspect of an electric field lightemitting device of the present invention.

FIG. 3 is a ¹H-NMR chart of TPAQn.

FIGS. 4( a)-4(b) are views showing an absorption-light emission spectrumof TPAQn.

FIGS. 5( a)-5(b) are views showing an absorption-light emission spectrumof CzQn.

FIG. 6 is a view showing luminance-current density (L-J) characteristicsof the electric field light emitting device of the present invention.

FIG. 7 is a view showing luminance-voltage (L-V) characteristics of theelectric field light emitting device of the present invention.

FIG. 8 is a view showing a light emission spectrum of the electric fieldlight emitting device of the present invention.

FIG. 9 is a view showing luminance-current density (L-J) characteristicsof the electric field light emitting device of the present invention.

FIG. 10 is a view showing luminance-voltage (L-V) characteristics of theelectric field light emitting device of the present invention.

FIG. 11 is a view showing a light emission spectrum of the electricfield light emitting device of the present invention.

FIG. 12 is a view showing current efficiency-luminance (η-L)characteristics of the electric field light emitting device of thepresent invention.

FIG. 13 is a view showing luminance-voltage (L-V) characteristics of theelectric field light emitting device of the present invention.

FIG. 14 is a view showing a light emission spectrum of the electricfield light emitting device of the present invention.

FIG. 15 is a view showing current-voltage (I-V) characteristics of theelectric field light emitting device of the present invention.

FIG. 16 is a view for explaining an organic semiconductor device inwhich the present invention is applied.

FIG. 17 is a cross-sectional view for explaining a light emittingapparatus in which the present invention is applied.

FIG. 18 is a plan view for explaining a light emitting apparatus inwhich the present invention is applied.

FIGS. 19( a)-19(c) are views for explaining an electronic device inwhich the present invention is applied.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS EmbodimentMode 1

As one aspect of the present invention, an electric field light emittingdevice which is an organic semiconductor device utilizing a quinoxalinederivative of the present invention will be explained with reference toFIG. 1.

In FIG. 1, there is shown a structure in which a first electrode 101 isformed on a substrate 100, an electric field light emitting layer 102 isformed on the first electrode 101, and a second electrode 103 is formedthereon.

A material to be employed for the substrate 100 can be a materialemployed in conventional electric field light emitting devices, and itcan be constituted for example of glass, quartz, transparent plastics orthe like.

In the present embodiment mode, the first electrode 101 functions as ananode, and the second electrode 103 functions as a cathode.

More specifically, the first electrode 101 is formed by an anodematerial, and the anode material employable in this case is preferably ametal, an alloy, an electrically conductive compound, and a mixturethereof having a large work function (work function equal to or higherthan 4.0 eV). As a specific example of the anode material, there can beused indium tin oxide (ITO), or indium zinc oxide (IZO) formed by mixingindium oxide with zinc oxide (ZnO) of 2-20%, or also gold (Au), platinum(Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron(Fe), cobalt (Co), copper (Cu), palladium (Pd) or a nitride of a metalmaterial (TiN).

On the other hand, as the cathode material to be used for forming thesecond electrode 103 there is preferably employed a metal, an alloy, anelectrically conductive compound, and a mixture thereof having a smallwork function (work function equal to or lower than 3.8 eV). Specificexamples of the cathode material include an element of the group 1 or 2of the periodic table, namely an alkali metal such as lithium (Li) orcesium (Cs), an alkali earth metal such as magnesium (Mg), calcium (Ca)or strontium (Sr), and an alloy including these (Mg:Ag, Al:Li). However,by forming a layer of a function promoting an electron injection betweenthe second electrode 103 and the light emitting layer and in laminationwith such second electrode, it is possible to use various conductivematerial such as Al, Ag, ITO as the second electrode 103 regardless ofthe magnitude of the work function.

For the layer of the function promoting the electron injection, acompound of an alkali metal or an alkali earth metal, such as lithiumfluoride (LiF), cesium fluoride (CsF) or calcium fluoride (CaF₂), can beused. In addition, it is also possible to use a material having anelectron transporting property, in which an alkali metal or an alkaliearth metal is contained, for example Alq containing magnesium (Mg).

The anode material and the cathode material mentioned above are formedas thin films by an evaporation method or a sputtering method, therebyrespectively forming the first electrode 101 and the second electrode103.

The electric field light emitting device of the present invention has astructure in which a light generated by a recombination of carriers inthe electric field light emitting layer 102 is emitted to the exteriorfrom either of the first electrode 101 and the second electrode 102, orboth thereof. Thus, in case the light is emitted from the firstelectrode 101, the first electrode 101 is formed with a lighttransmitting material, and, in case the light is emitted from the sideof the second electrode 103, the second electrode 103 is formed with alight transmitting material.

The electric field light emitting layer 102 is formed by laminatingplural layers, and, in the present embodiment mode, it is formed bylaminating a hole injecting layer 111, a hole transporting layer 112, alight emitting layer 113 and an electron transporting layer 114.

As a hole injecting material for forming the hole injecting layer 111, acompound of phthalocyanine type is effective. For example,phthalocyanine (abbreviation: H₂Pc), copper phthalocyanine(abbreviation: CuPc) etc., can be employed.

As a hole transporting material for forming the hole transporting layer112, a compound of aromatic amine type (namely having a benzenering-nitrogen bond) is suitable. Widely employed materials include, forexample, 4,4′-bis[N-(3-methylphenyl)-N-phenyl-amino]-biphenyl(abbreviation: TPD), or its derivatives such as4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (abbreviation: α-NPD),or star burst aromatic amine compounds, such as4,4′,4″-tris(N,N-diphenyl-amino)-triphenylamine (abbreviation: TDATA),or 4,4′,4″-tris[N-(3-methylphenyl)-N-phenyl-amino]-triphenylamine(abbreviation: MTDATA).

The light emitting layer 113 is formed by the quinoxaline derivative ofthe present invention represented by the general formula (1), (2) or(6). The quinoxaline derivative of the present invention, having abipolar property and a light emitting property, can be employed as thelight emitting layer without a particular doping with a guest materialhaving a light emitting property.

The quinoxaline derivative of the present invention is considered tohave a bipolar character, as an arylamine skeleton of an electrondonating property is introduced into a quinoxaline skeleton having anelectron transporting property.

As an electron transporting material in case of forming the electrontransporting layer 114, a metal complex having a quinoline skeleton or abenzoquinoline skeleton is preferable, such astris(8-quinolinolato)aluminum (abbreviation: Alq₃),tris(5-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]-quinolinato)beryllium (abbreviation: BeBq₂), orBAlq mentioned above. There is also available a metal complex having anoxazole or thiazole ligand, such asbis[2-(2-hydroxyphenyl)-benzoxazolato]zinc (abbreviation: Zn(BOX)₂) orbis[2-(2-hydroxyphenyl-benzothiazolato)zinc (abbreviation: Zn(BTZ)₂). Inaddition to the metal complex,2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: TAZ),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenyl)-1)-1,2,4-triazole(abbreviation: p-EtTAZ), basophenanthroline (abbreviation: BPhen),basocuproin (abbreviation: BCP), and the like can be used as theelectron transporting material.

Based on the foregoing, an electric field light emitting device can beprepared with the light emitting layer 113 formed by the quinoxalinederivative of the present invention, the hole injecting layer 111, thehole transporting layer 112, and the electron transporting layer 114formed by a low molecular material. The hole injecting layer 111, thehole transporting layer 112, and the electron transporting layer 114 arenot limited to a low molecular material, but can also be formed by ahigh molecular material.

In the present embodiment mode, the electric field light emitting deviceis formed on the substrate 100, but the electric field light emittingdevice may also be formed, as shown in FIG. 2, on a thin film transistor(TFT), with an electrical connection to the TFT. In FIG. 2, 10 indicatesa substrate, broken-lined areas 11, 12 indicate TFT, 14 indicates afirst electrode, 15 indicates a layer containing a light emittingsubstance, 16 indicates a second electrode, and 17 indicates a wiring,wherein a laminated portion of the first electrode 14, the layer 15containing the light emitting substance and the second electrode 16functions as a light emitting device 13. Thus there can be prepared alight emitting apparatus of active matrix type in which the drive of thelight emitting device is controlled by the TFT. The structure of the TFTis not particularly restricted and can be a top gate type or a bottomgate type.

The electric field light emitting layer, in addition to the structureshown in the present embodiment mode, may also have a laminatedstructure such as hole injecting layer\light emitting layer\electroninjecting layer. Also since the quinoxaline derivative of the presentinvention has a hole transporting property and an electron transportingproperty, and also a light emitting property, the electric field lightemitting layer may have a structure utilizing the quinoxaline derivativeof the present invention in a single layer.

The quinoxaline derivative of the present invention, being a materialhaving a bipolar property and a light emitting property, can beemployed, as indicated in the present embodiment mode, as a lightemitting layer without including a dopant (guest material) or the like.Also owing to the bipolar property, the light emitting portion is noteasily deviated at the interface of the laminated films, and an electricfield light emitting device of a satisfactory light emitting propertycan be prepared with little change in the light emission spectrum andlittle decrease in the light emission efficiency resulting from aninteraction such as an exciplex. Also as the contained microcrystallinecomponent is very few in the film formation to provide a satisfactoryfilm forming property, there can be prepared a satisfactory electricfield light emitting device with low device defects such as a dielectricbreakdown by an electric field concentration. Also the quinoxalinederivative of the present invention, being a material having a carriertransporting property (electron transporting property and holetransporting property), can reduce, by the use in the light emittinglayer, a drive voltage of the electric field light emitting device.

Embodiment Mode 2

This embodiment mode explains an electric field light emitting deviceemploying the quinoxaline derivative of the present invention as a guestmaterial.

The quinoxaline derivative of the present invention, having a lightemitting property, can also be used as a guest material (light emitter)for obtaining a light emission of blue to blue-green color.

The quinoxaline derivative of the present invention, being a materialhaving a carrier transporting property, can reduce, by the use as aguest material, a drive voltage of the electric field light emittingdevice.

In such case, there can be adopted a device structure having an electricfield light emitting layer (a structure of single layer or laminatedlayers) employing, as a light emitting layer, an organic compound layercontaining the quinoxaline derivative represented by the general formula(1), (2) or (6), sandwiched between a pair of electrodes (an anode and acathode). For example, in an electric field light emitting device havinga device structure of anode\hole injecting layer\hole transportinglayer\light emitting layer\electron transporting layer\cathode,anode\hole injecting layer\light emitting layer\electron transportinglayer\cathode, anode\hole injecting layer\hole transporting layer\lightemitting layer\electron transporting layer\electron injectinglayer\cathode, anode\hole injecting layer\hole transporting layer\lightemitting layer\hole blocking layer\electron transporting layer\cathode,or anode\hole injecting layer\hole transporting layer\light emittinglayer\hole blocking layer\electron transporting layer\electron injectinglayer\cathode, a light emitting layer containing the quinoxalinederivative represented by the general formula (1), (2) or (6) as a guestmaterial can be used.

As the host material, a known material can be employed such as, inaddition to the hole transporting material and the electron transportingmaterial described in the embodiment mode 1,4,4′-bis(N-carbazolyl)-biphenyl (abbreviation: CBP),2,2′,2″-(1,3,5-benzenetri-yl)-tris[1-phenyl-1H-benzimidazole](abbreviation: TPBI), or 9,10-di(2-naphthyl)anthracene (abbreviation:DNA).

In particular, a quinoxaline derivative represented by the foregoingstructural formula (10) as a guest material and DNA as a host materialallow to obtain a high light emitting efficiency and a light emission ofhighly pure blue color.

The electric field light emitting device of the present embodiment modecan be prepared, as shown in the embodiment mode 1, on a substrate orcan be prepared on a TFT as an electric field light emitting deviceelectrically connected with the TFT.

Embodiment Mode 3

The present embodiment mode explains an electric field light emittingdevice employing the quinoxaline derivative of the present invention asa host material.

The quinoxaline derivative of the present invention, having a bipolarproperty and showing very few microcrystalline component contained in afilm formation thereby providing a satisfactory film forming property,can be used as a host material.

Also the quinoxaline derivative of the present invention, being amaterial having a carrier transporting property as explained in theforegoing, can reduce, when employed as a host material, a drive voltageof the electric field light emitting element.

In case of use as a host material, there can be obtained a lightemission color resulting from a guest material, or a mixed lightemission color of a light emission color resulting from the quinoxalinederivative of the present invention and a light emission color resultingfrom the guest material doped in such quinoxaline derivative.

In such case, there can be adopted a device structure having an electricfield light emitting layer (a structure of single layer or laminatedlayers) employing, as a light emitting layer, an organic compound layercontaining the quinoxaline derivative represented by the general formula(1), (2) or (6), sandwiched between a pair of electrodes (anode andcathode). For example, in an electric field light emitting device havinga device structure of anode\hole injecting layer\hole transportinglayer\light emitting layer\electron transporting layer\cathode,anode\hole injecting layer\light emitting layer\electron transportinglayer\cathode, anode\hole injecting layer\hole transporting layer\lightemitting layer\electron transporting layer\electron injectinglayer\cathode, anode\hole injecting layer\hole transporting layer\lightemitting layer\hole blocking layer\electron transporting layer\cathode,or anode\hole injecting layer\hole transporting layer\light emittinglayer\hole blocking layer\electron transporting layer\electron injectinglayer\cathode, a light emitting layer containing the quinoxalinederivative represented by the general formula (1), (2) or (6) as a hostmaterial can be used.

As the guest material, a known material can be used, for example afluorescent material such as4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran(abbreviation: DCM1),4-(dicyanomethylene)-2-methyl-6-(julolidin-4-yl-vinyl)-4H-pyran(abbreviation: DCM2), N,N-dimethylquinacridone (abbreviation: DMQd),9,10-diphenylanthracene (abbreviation: DPA), 5,12-diphenyltetracene(abbreviation: DPT), coumarin 6, perylene or rubrene, or aphosphorescent material such asbis(2-(2′-benzothienyl)pyridinato-N,C^(3′))(acetylacetonato) iridium(abbreviation: Ir(btp)₂(acac)) or the like.

An electric field light emitting device for obtaining a light emissionfrom a triple excited state by adding a phosphorescent material such asthe aforementioned iridium complex is already known as a device capableof attaining a high efficiency, but a high drive voltage has been adrawback. However, the quinoxaline derivative of the present inventionemployed as the host allows to reduce the drive voltage.

Also the quinoxaline derivatives of the present invention relativelyfrequently show the light emission in a range of blue to green-yellowcolor. Therefore, in case of adding a phosphorescent material to thequinoxaline derivative of the present invention as a host, thephosphorescent material preferably has a light emitting wavelength at alonger wavelength than in the quinoxaline derivative, particularly in arange of yellow to red color such as about 560 to 700 nm. However suchcondition is not restrictive as the light emission wavelength of thequinoxaline derivative can be changed by a substituent effect.

The electric field light emitting device of the present embodiment modecan be prepared, as shown in the embodiment mode 1, on a substrate orcan be prepared on a TFT as an electric field light emitting deviceelectrically connected with the TFT.

Embodiment Mode 4

The present embodiment mode 4 illustrates a mode in which thequinoxaline derivative of the present invention is used as an activelayer of a vertical type transistor (SIT) which is one of organicsemiconductor derives.

The device has a structure in which, as shown in FIG. 16, an activelayer 1202 of a thin film shape formed by the quinoxaline derivative ofthe present invention is sandwiched between a source electrode 1201 anda drain electrode 1203, and a gate electrode 1204 is embedded in theactive layer 1202. 1205 indicates means for applying a gate voltage, and1206 indicates means for controlling a voltage between the source andthe drain.

In such device structure, when a voltage is applied between the sourceand the drain in a state in which a gate voltage is not applied, acurrent flows as in the electric field light emitting device (on-state).When a gate voltage is applied in such state, a depletion layer isgenerated in the vicinity of the gate electrode 1204, whereby thecurrent no longer flows (off-state). A function as a transistor isobtained through the above-described mechanisms.

In a vertical type transistor, as in the electric field light emittingdevice, a material having a carrier transporting property and asatisfactory film forming property is required for the active layer, andthe quinoxaline derivative of the present invention sufficiently meetsthese conditions and is therefore useful.

Embodiment Mode 5

As the light emitting device of the present invention functions at a lowdrive voltage, a light emitting apparatus employing the presentinvention can be operated with a low electric power consumption. Also anelectronic device utilizing such light emitting apparatus employing thepresent invention can be operated with a low electric power consumption.

Thus, the present embodiment mode explains a light emitting apparatusand an electronic device employing the present invention, with referenceto FIGS. 17-19.

A light emitting apparatus formed by providing a plurality of the lightemitting device of the present invention on a substrate can beinstalled, after mounting an external input terminal and sealing, as adisplay apparatus in various electronic devices.

The present embodiment mode explains a light emitting apparatus aftersealing and an electronic device mounted with such light emittingapparatus, with reference to FIGS. 17-19. However, FIGS. 17-19 merelyshow an embodiment mode, and the structure of the light emittingapparatus is not limited to such structure.

FIG. 17 is a cross-sectional view of a light-emitting apparatus aftersealing. A substrate 6500 and a sealing substrate 6501 are adhered witha sealing agent 6502 so as to enclose a transistor 6504 and alight-emitting device 6505. At an end portion of the substrate 6500, anFPC (flexible printed circuit) 6503 constituting an external inputterminal is mounted. An internal region enclosed by the substrate 6500and the sealing substrate 6501 is filled with an inert gas such asnitrogen or a resinous material.

FIG. 18 is a schematic view, seen from above, of a light emittingapparatus in which the present invention is applied. Referring to FIG.18, a broken-lined area 6510 indicates a drive circuit portion (sourceside drive circuit), 6511 indicates a pixel portion, and 6512 indicatesa drive circuit portion (gate side drive circuit). In the pixel portion6511, light emitting devices of the present invention are provided. Thedrive circuit portions 6510 and 6512 are connected by the FPC 6503constituting the external input terminal and a group of wirings formedon the substrate 6500. By receiving a video signal, a clock signal, astart signal, a reset signal etc. from the FPC (flexible printedcircuit) 6503, signals are entered into the source side drive circuit6510 and the gate side drive circuit 6512. A printed wiring board (PWB)6513 is mounted on the FPC 6503. The drive circuit portion 6510 includesa shift register 6515, a switch 6516, and memories (latches) 6517, 6518,while the drive circuit portion 6512 includes a shift register 6519 anda buffer 6520. Also other functions may further be provided. Also thedrive circuit portion need not be provided on the same substrate as thatfor the pixel portion 6511, and it may be provided outside thesubstrate, for example utilizing a TCP in which an IC chip is mounted onan FPC in which a wiring pattern is formed.

FIG. 19 shows an embodiment of an electronic device in which a lightemitting apparatus embodying the present invention is mounted.

FIG. 19(A) is a notebook type personal computer prepared applying thepresent invention, and is constituted by a main body 5521, a casing5522, a display portion 5523, a keyboard 5524 etc. The personal computercan be completed by incorporating, as a display portion, a lightemitting apparatus having the light emitting device of the presentinvention.

FIG. 19(B) is a portable telephone prepared applying the presentinvention, and a main body 5552 is constituted by a display portion5551, an audio output portion 5554, an audio input portion 5555,operation switches 5556, 5557, an antenna 5553 etc. The portabletelephone can be completed by incorporating, as a display portion, alight emitting apparatus having the light emitting device of the presentinvention.

FIG. 19(C) is a television receiver prepared applying the presentinvention, and is constituted of a display portion 5531, a casing 5532,a speaker 5533 etc. The television receiver can be completed byincorporating, as a display portion, a light emitting apparatus havingthe light emitting device of the present invention.

As explained above, the light emitting apparatus of the presentinvention is suitable for use as a display portion of various electronicdevices.

The present embodiment describes a notebook type personal computer, butthe light emitting apparatus having the light emitting device of thepresent invention may also be mounted in a car navigation or anilluminating apparatus.

EMBODIMENTS Embodiment 1 Synthesis Example 1

This synthesis example 1 specifically shows a synthesis example of thequinoxaline derivative of the present invention represented by theforegoing structural formula (10) (hereinafter represented as TPAQn).

Synthesis of 2,3-bis(4-bromophenyl)quinoxaline

At first 10 g (27.4 mmol) of 4-bromobenzyl and 3.5 g (33.5 mmol) ofo-phenylenediamine were charged in a 500 ml-eggplant-shaped flask, andagitated and refluxed in chloroform for 8 hours.

Then, after cooling to the room temperature, remainingo-phenylenediamine was eliminated by column chromatography whereby2,3-bis(4-bromophenyl)quinoxaline was obtained.

Synthesis of TPAQn

Then, 4.40 g (10.0 mmol) of thus obtained2,3-bis(4-bromophenyl)quinoxaline were weighed and charged in athree-necked flask, and dissolved in 75 ml of toluene under a nitrogenflow. Then, 0.22 g (0.2 mmol) of Pd(dba)₂, 2.88 g (30 mmol) of NaO-t-Buand 3.46 g (20.4 mmol) of diphenylamine were added, also 1.8 ml of a 10wt. % hexane solution of tri(t-butylphosphin) and agitation under heatwas executed for 8 hours at 80° C.

Then, after cooling to the room temperature, the reaction is terminatedby adding water, and an extraction was made with chloroform. Then, afterwashing with saturated salt solution, a drying was executed with MgSO₄.Thereafter, a recrystallization was executed from chloroform to obtaindesired TPAQn (yellow-green crystal, yield 2.7 g (yield: 44%)). FIG. 3shows a ¹H-NMR chart of TPAQn. The obtained TPAQn had a decompositiontemperature of 411° C. and was easily capable of film formation by avacuum evaporation method by a resistance heating. A uniform film wasformed without crystallization, coagulation or the like. In ameasurement with a differential scanning calorimeter (Pyris 1DSC,manufactured by Perkin Elmer Inc.), a glass transition point wasobserved at 93° C. and a melting point was observed in two positions at214 and 220° C.

An absorption-light emission spectrum of TPAQn in a toluene solution isshown in FIG. 4( a), and an absorption-light emission spectrum of a thinfilm is shown in FIG. 4( b). In the toluene solution, a blue lightemission having a peak at 480 nm was obtained, and, in the thin filmstate, a blue-green light emission having a peak at 500 nm was obtained.Also a HOMO level in a thin film state, measured by a photoelectronspectroscopy (AC-2, manufactured by Riken Keiki Co.) in the air, was−5.46 eV. Also, taking an absorption end of the absorption spectrumshown in FIG. 4( b) as an energy gap, a LUMO level was −2.76 eV.

Also when a carrier mobility of the evaporated film of TPAQn wasmeasured by a time of flight (TOF) method, a hole mobility was in theorder of 10⁻⁶ cm²/Vs, and an electron mobility was in the order of 10⁻⁵cm²/Vs. Based on these facts, it was identified that TPAQn was excellentin the transporting property for both hole and electron carriers, andalso had a bipolar property.

Synthesis Example 2

A quinoxaline derivative of the present invention represented by theforegoing structural formula (38) (hereinafter represented as CzQn) canbe obtained by employing carbazole instead of diphenylamine in thesynthesis example 1.

The obtained CzQn had a decomposition temperature of 447° C. and waseasily capable of film formation by a vacuum evaporation method by aresistance heating. A uniform film was formed without crystallization,coagulation or the like.

An absorption-light emission spectrum of CzQn in a toluene solution isshown in FIG. 5( a), and an absorption-light emission spectrum of a thinfilm is shown in FIG. 5( b). In the solution, a purple-blue lightemission having a peak at 440 nm was obtained, and, in the thin filmstate, a blue light emission having a peak at 460 nm was obtained. Alsoa HOMO level in a thin film state, measured by a photoelectronspectroscopy (AC-2, manufactured by Riken Keiki Co.) in the air, was−5.94 eV. Also, taking an absorption end of the absorption spectrumshown in FIG. 5( b) as an energy gap, a LUMO level was −3.02 eV.

Synthesis Example 3

A quinoxaline derivative of the present invention represented by theforegoing structural formula (50) (hereinafter represented as PoxQn) canbe obtained by employing phenoxazine instead of diphenylamine in thesynthesis example 1.

The obtained PoxQn had a decomposition temperature of 434° C. and waseasily capable of film formation by a vacuum evaporation method by aresistance heating. A uniform film was formed without crystallization,coagulation or the like.

A light emission spectrum of PoxQn in a toluene solution had a peak at556 nm and in a thin film state had a peak at 561 nm, both green-yellowlight emission. Measurements of a HOMO level and a LUMO level in a thinfilm state in a method similar to that in the synthesis example 1provided a HOMO level of −5.59 eV and a LUMO level of −3.11 eV.

Synthesis Example 4

A quinoxaline derivative of the present invention represented by theforegoing structural formula (56) (hereinafter represented as PthQn) canbe obtained by employing phenothiazine instead of diphenylamine in thesynthesis example 1.

The obtained PthQn had a decomposition temperature of 428° C. and waseasily capable of film formation by a vacuum evaporation method by aresistance heating. A uniform film was formed without crystallization,coagulation or the like.

A light emission spectrum of PthQn in a toluene solution was a yellowlight emission having a peak at 575 nm and in a thin film state was agreen-yellow light emission having a peak at 554 nm. Measurements of aHOMO level and a LUMO level in a thin film state in a method similar tothat in the synthesis example 1 provided a HOMO level of −5.53 eV and aLUMO level of −2.81 eV.

Synthesis Example 5

A quinoxaline derivative of the present invention represented by theforegoing structural formula (27) (hereinafter represented as NPADiBzQn)can be obtained by employing 9,10-phenanthrenediamine instead ofo-phenylenediamine and N-(1-naphthyl)-N-phenylamine instead ofdiphenylamine in the synthesis example 1.

The obtained NPADiBzQn had a decomposition temperature of 460° C. andwas easily capable of film formation by a vacuum evaporation method by aresistance heating. A uniform film was formed without crystallization,coagulation or the like.

A light emission spectrum of NPADiBzQn in a toluene solution was a bluelight emission having a peak at 469 nm and in a thin film state was ablue-green light emission having a peak at 490 nm. Measurements of aHOMO level and a LUMO level in a thin film state in a method similar tothat in the synthesis example 1 provided a HOMO level of −5.55 eV and aLUMO level of −2.91 eV.

Embodiment 2

This embodiment provides a specific example of an electric field lightemitting device employing a light emitting layer constituted solely ofthe quinoxaline derivative (TPAQn) of the present invention obtained inthe foregoing synthesis example 1. The device structure was made similarto that shown in FIG. 1.

At first, there was employed a substrate 100 in which an ITO film of 110nm was formed as a first electrode 101 on a glass. The ITO was so formedas to function in an electrode of a size of 2 mm square. The ITOfunctions as an anode.

Then films of CuPc of 20 nm as a hole injecting layer 111, α-NPD of 30nm as a hole transporting layer 112 and TPAQn of 30 nm as a lightemitting layer 113 were formed. Further, BCP of 20 nm and Alq of 20 nmwere laminated in succession as an electron transporting layer 114.Further, in the present embodiment, after calcium fluoride of 2 nm as alayer for promoting electron injection was laminated on the electrontransporting layer 114, aluminum (Al) of 100 nm was laminated as asecond electrode 103 to obtain an organic semiconductor device (electricfield light emitting device) of the present invention.

Luminance-current density (L-J) characteristics and luminance-voltage(L-V) characteristics of the obtained device are respectively shown inFIGS. 6 and 7. This device, under an application of a voltage of 9.4 V,showed a current of a current density of 21.9 mA/cm² and a lightemission at a luminance of 1030 cd/m². A current efficiency was 4.71cd/A.

Also a light emission spectrum of this device is shown in FIG. 8. Asshown in FIG. 8, there was obtained a blue-green light emission having amaximum peak value at about 500 nm.

Embodiment 3

This embodiment provides a specific example of an electric field lightemitting device employing a quinoxaline derivative (TPAQn) of thepresent invention obtained in the foregoing synthesis example 1 as aguest material of the light emitting layer. The device structure wasmade similar to that shown in FIG. 1, but materials for forming thelayers were made different from those in Embodiment 1.

At first, there was employed a substrate 100 in which an ITO film of 110nm was formed as a first electrode 101 on a glass. The ITO was so formedas to function in an electrode of a size of 2 mm square. The ITOfunctions as an anode.

Then films of CuPc of 20 nm as a hole injecting layer 111, and α-NPD of30 nm as a hole transporting layer 112 were formed. Then a lightemitting layer 113 of 30 nm was formed by co-evaporating DNA and TPAQnso as to obtain a weight ratio of 4:0.3 (namely TPAQn constituted about7 wt. %). Further, BCP of 20 nm was formed as an electron transportinglayer 114, then calcium fluoride of 2 nm as a layer for promotingelectron injection was laminated on the electron transporting layer 114,and aluminum (Al) of 100 nm was laminated as a second electrode 103 toobtain an organic semiconductor device (electric field light emittingdevice) of the present invention.

Luminance-current density (L-J) characteristics and luminance-voltage(L-V) characteristics of the obtained device are respectively shown inFIGS. 9 and 10. This device, under an application of a voltage of 8.2 V,showed a current of a current density of 20.2 mA/cm² and a lightemission at a luminance of 1025 cd/m². A current efficiency was 5.08cd/A.

Also a light emission spectrum of this device is shown in FIG. 11. Asshown in FIG. 11, there was obtained a blue light emission having amaximum peak value at about 480 nm.

Embodiment 4

This embodiment provides a specific example of an electric field lightemitting device employing a quinoxaline derivative (TPAQn) of thepresent invention obtained in the foregoing synthesis example 1 as ahost material of the light emitting layer. There is particularly shownan example of a device utilizing a phosphorescent material showing alight emission from a triplet excited state. The device structure wasmade similar to that shown in FIG. 1, but materials for forming thelayers were made different from those in Embodiment 1.

At first, there was employed a substrate 100 in which an ITO film of 110nm was formed as a first electrode 101 on a glass. The ITO was so formedas to function in an electrode of a size of 2 mm square. The ITOfunctions as an anode.

Then films of CuPc of 20 nm as a hole injecting layer 111, and α-NPD of30 nm as a hole transporting layer 112 were formed. Then a lightemitting layer 113 of 30 nm was formed by co-evaporating TPAQn andIr(btp)₂(acac) in such a manner that Ir(btp)₂(acac) was contained byabout 8.8 wt. %. Further, BCP of 10 nm and Alq of 20 nm were laminatedin succession as an electron transporting layer 114. Also calciumfluoride of 2 nm as a layer for promoting electron injection waslaminated on the electron transporting layer 114, and aluminum (Al) of100 nm was laminated as a second electrode 103 to obtain an organicsemiconductor device (electric field light emitting device) of thepresent invention.

Current efficiency-luminance (η-L) characteristics and luminance-voltage(L-V) characteristics of the obtained device are respectively indicatedby “Embodiment 4” in FIGS. 12 and 13. This device had a drive voltage of7.2 V at a light emission with a luminance of about 200 cd/m², with acurrent of a current density of 4.58 mA/cm². A current efficiency was4.14 cd/A.

Also a light emission spectrum of this device is shown in FIG. 14. Basedon the shape of the spectrum, the light emission was identified from thephosphorescent material Ir(btp)₂(acac). The CIE chromaticity coordinateswere (x, y)=(0.31, 0.69), and it was a red light emission withsatisfactory chromaticity.

As explained in the foregoing, the current efficiency was 4.14 cd/A at200 cd/m², and there was realized a device of a very high efficiency asa red light emitting device. Such high efficiency is a feature of thedevice utilizing a phosphorescent material, and the device of thepresent embodiment fully exploits such feature. Therefore, thequinoxaline derivative of the present invention is suitable as a hostmaterial in a light emitting layer utilizing a phosphorescent material.

Comparative Example 1

For the purpose of comparison with Embodiment 4, there is shown anexample of characteristics of a conventional electric field lightemitting device employing Ir(btp)₂(acac) as a guest. The devicestructure was similar to Embodiment 4, except for the light emittinglayer 113. The light emitting layer 113 had a conventional structurewith CBP as a host, and an addition concentration of Ir(btp)₂(acac) wasselected as about 7.5 wt %.

Current efficiency-luminance (η-L) characteristics and luminance-voltage(L-V) characteristics of the obtained device are respectively indicatedby “Comparative example 1” in FIGS. 12 and 13. This device had a drivevoltage of 9.0 V at a light emission with a luminance of about 200cd/m², with a current of a current density of 5.55 mA/cm². A currentefficiency was 3.55 cd/A.

Also a light emission spectrum of this device was about same as in FIG.14. The CIE chromaticity coordinates were (x, y)=(0.31, 0.67).

In comparison with Embodiment 4, the light emission spectrum and thechromaticity were about same, but the current efficiency was somewhatinferior (FIG. 12). Thus, the quinoxaline derivative of the presentinvention proved to be more suitable material than the conventionalmaterial, as a host material of the light emitting layer.

Also this comparative example 1 had a higher drive voltage in comparisonwith Embodiment 4 (FIG. 13). For example the drive voltage for attainingabout 200 cd/m² was 9.0 V which was higher by 1.8 V than in Embodiment 4(7.2 V). Therefore the use of the quinoxaline derivative of the presentinvention as the host material enabled to reduce the drive voltage thanin the conventional art.

FIG. 15 shows current-voltage (I-V) characteristics of Embodiment 4 andComparative example 1. Embodiment 4 shows an apparent shift to a lowervoltage side, indicating a higher current flowability. This factindicates that the quinoxaline derivative of the present invention issuperior to CBP in the carrier transporting property, thus contributingto a decrease in the drive voltage. Thus, the quinoxaline derivative ofthe present invention, having an excellent carrier transportingproperty, can be considered to similarly decrease the drive voltage alsoin case of being employed as a host material for other various lightemitting materials.

Based on the foregoing, it was identified that the use of thequinoxaline derivative of the present invention as the host material inthe light emitting layer could reduce the drive voltage. It wasparticularly identified, in the use as the host material of thephosphorescent material, that an electric field light emitting devicecould be realized with a higher efficiency and a lower drive voltagethan in the conventional art.

Embodiment 5

This embodiment provides a specific example of an electric field lightemitting device employing a quinoxaline derivative (TPAQn) of thepresent invention obtained in the foregoing synthesis example 1 as ahost material of the light emitting layer. There is particularly shownan example of a device utilizing a phosphorescent material showing alight emission from a triplet excited state as a guest. The devicestructure was made same as in Embodiment 4, except that BCP waseliminated therefrom.

At first, there was employed a substrate 100 in which an ITO film of 110nm was formed as a first electrode 101 on a glass. The ITO was so formedas to function in an electrode of a size of 2 mm square. The ITOfunctions as an anode.

Then films of CuPc of 20 nm as a hole injecting layer 111, and α-NPD of40 nm as a hole transporting layer 112 were formed. Then a lightemitting layer 113 of 30 nm was formed by co-evaporating TPAQn andIr(btp)₂(acac) in such a manner that Ir(btp)₂(acac) was contained byabout 1.0 wt. %. Further, Alq of 20 nm was laminated as an electrontransporting layer 114. Also calcium fluoride of 2 nm as a layer forpromoting electron injection was laminated on the electron transportinglayer 114, and aluminum (Al) of 100 nm was laminated as a secondelectrode 103 to obtain an organic semiconductor device (electric fieldlight emitting device) of the present invention.

Current efficiency-luminance (η-L) characteristics and luminance-voltage(L-V) characteristics of the obtained device are respectively indicatedby “Embodiment 5” in FIGS. 12 and 13. This device had a drive voltage of6.6 V at a light emission with a luminance of about 200 cd/m², with acurrent of a current density of 5.79 mA/cm². A current efficiency was3.44 cd/A.

Also a light emission spectrum of this device was similar to thespectrum shown in FIG. 14. The CIE chromaticity coordinates were (x,y)=(0.32, 0.68), and it was a red light emission with satisfactorychromaticity.

The current efficiency was similar to the conventional art (Comparativeexample 1), and there was realized a device of a very high efficiency asa red light emitting device (FIG. 12). Also from FIG. 13 it can beunderstood that the drive voltage is very low in comparison withComparative example 1. For example, the drive voltage for attainingabout 200 cd/m² was 6.6 V which was lower by as much as 2.4 V incomparison with 9.0 V in Comparative example 1. The I-V characteristicsshown in “Embodiment 5” in FIG. 15 also shows a shift to a lower voltageside in comparison with the conventional art (Comparative example 1),and the high carrier transporting property of the quinoxaline derivativeof the present invention is considered to contribute to the decrease inthe drive voltage.

It is particularly to be noted that a highly efficient device isrealized without utilizing BCP which is applied in the electrontransporting layer of Embodiment 4 and Comparative example 1. In adevice causing light emission of a phosphorescent material, it hasnormally been considered necessary to provide, next to the lightemitting layer, an electron transporting layer (so-called hole blockinglayer) constituted of a material capable of enclosing holes or excitons,namely a hole blocking material or an exciton blocking material, such asBCP in Embodiment 4 or Comparative example 1. This is because, withoutsuch layer, the excitation energy of the phosphorescent material istransferred to the ordinarily employed material of the electrontransporting layer such as Alq, so that an efficient light emissioncannot be obtained from the phosphorescent material.

However, according to present Embodiment 5, in case of employing thequinoxaline derivative of the present invention as the host material tothe phosphorescent material, it is unnecessary to provide so-called holeblocking layer and made possible to decrease the number of layers. Alsoa hole blocking material or an exciton blocking material such as BCPgenerally shows a severe crystallization and results in a deteriorationof reliability, so that the result of Embodiment 5 allowing to dispensewith such materials leads to an advantage of an improvement in thereliability of the electric field light emitting device utilizing thephosphorescent material.

Furthermore, the result of Embodiment 5 indicates that the efficiency ofthe energy transfer from the quinoxaline derivative of the presentinvention to the phosphorescent material is extremely satisfactory. Alsoin this sense, the quinoxaline derivative of the present invention issuitable as a host material for the light emitting layer employing thephosphorescent material.

1. A quinoxaline derivative represented by a structural formula (14).


2. An electric field light emitting device comprising a quinoxalinederivative represented by a structural formula (14) between a pair ofelectrodes.


3. A host material including the quinoxaline derivative according toclaim
 1. 4. An organic semiconductor device, wherein the quinoxalinederivative according to claim 1 is included in an active layer.
 5. Anelectronic device comprising the organic semiconductor device accordingto claim
 4. 6. An electronic device according to claim 5, wherein theelectronic device is any one of a personal computer, a portabletelephone and a television receiver.
 7. An electric field light emittingdevice comprising a light emitting layer containing a quinoxalinederivative represented by a structural formula (14) and a phosphorescentmaterial showing a light emission from a triplet excited state between apair of electrodes.


8. An electric field light emitting device according to claim 7, whereina light emission spectrum of the phosphorescent material has a peak from560 to 700 nm.
 9. An electronic device employing the electric fieldlight emitting device according to claim
 7. 10. An electronic deviceaccording to claim 9, wherein the electronic device is any one of apersonal computer, a portable telephone and a television receiver. 11.An illuminating apparatus comprising a quinoxaline derivativerepresented by a structural formula (14) between a pair of electrodes.